align error response with api spec

[geospatial-jeff]

Related Issue(s):

• Error response invalid #360

Description:
Aligns responses from exception handlers with what is expected by the spec. After running docker-compose up and sending a /collections/abc request, the application will now return:

{
    "code": "NotFoundError",
    "description": "Collection abc not found"
}

PR Checklist:

• Code is formatted and linted (run pre-commit run --all-files)
• Tests pass (run make test)
• Documentation has been updated to reflect changes, if applicable, and docs build successfully (run make docs)
• Changes are added to the CHANGELOG.